This invention is directed to a blend of a crystalline poly(aryl ether ketone) and a polyarylate and/or a liquid crystalline polyarylate. These blends exhibit improved mechanical properties and environmental stress rupture resistance.
Poly(aryl ether ketones) are high performance materials which are useful for various demanding applications. They offer a combination of excellent thermal stability, hydrolytic stability, excellent chemical and environmental stress rupture resistance. This combined with very high crystalline melting points yields a property balance not available with other classes of polymers.
In the early 1980's, a poly(aryl ether ketone) of the following formula was made commercially available, e.g. U.S. Pat. No. 4,320,224: ##STR1##
The poly(aryl ether ketone) of the following formula is known from the literature, e.g. U.S. Pat. No. 3,956,240: ##STR2##
Another poly(aryl ether ketone) which was available commercially is of the following formula. e.g. U.S. Pat. No. 3,953,400: ##STR3##
The poly(aryl ether ketones) are crystalline polymers which exhibit high melting points. Due to their high melting points, high processing temperatures are required (&gt;300.degree. C.) in order to fabricate the polymer. Few polymeric materials currently available are stable enough to be blended with the poly(aryl ether ketones) at such high temperatures.
Polyarylates are aromatic polyesters, many of which are derived from a dihydric phenol, particularly 2,2-bis(4-hydroxyphenyl) propane (also identified as Bisphenol-A) and an aromatic dicarboxylic acid(s), particularly mixtures of terephthalic and isophthalic acids. A preferred polyarylate is of the following formula: ##STR4##
Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties including high impact strength. The polyarylates have good melt stability at high temperatures.
In the present invention it has been found that a blend of a poly(aryl ether ketone) and a polyarylate has both a notched izod impact strength and tensile impact strength which is significantly higher than that of either of the unblended constituents. Further, the addition of poly(aryl ether ketone) to polyarylate results in a significant improvement in the environmental stress rupture resistance of the polyarylate. Also, the addition of a liquid crystalline polyarylate to a poly(aryl ether ketone) leads to improved strength.
U.S. Pat. No. 4,438,236 issued Mar. 20, 1984 describes a composition containing a melt-processable polymer and an anisotropic melt-forming polymer. Specifically, Example 6 describes blending a polyether-etherketone with a liquid crystal polyester which was copoly (chloro-1,4-phenylene ethylene dioxy-4,4'dibenzoate) terephthalate. This example states that this blend has a significant reduction in melt viscosity as compared to the polyetheretherketone polymer itself.
However, it has been found that the addition of liquid crystalline polyarylates to poly(aryl ether ketone)s leads to a decrease in melt flow (increase in viscosity) at both low and high shear rates. The blends of this invention exhibit a higher viscosity than the constituent polymers. This is contrary to the disclosure of U.S. Pat. No. 4,438,236, which states that the addition of small amounts of liquid crystalline polymers to many diverse polymer systems leads to increased melt flow (decreased viscosity). In the instant blend, some unexpected interaction between the liquid crystalline polyarylate and the poly(aryl ether ketone) must be occurring.
European Patent Application No. 59077 published Sept. 1, 1982 describes a method for the orientation of films made from a thermoplastic polyether ether ketone. This publication states that the polymer may also contain, for the purpose of improving the fluidity in extrusion processing, up to 50 wt. % of heat resistant polymers such as polyarylene polyether polysulfone, polyarylate, polyester, nylon or polycarbonate, or a polyolefin such as polyethylene or polypropylene. However, many of these blends would not be stable at the temperatures needed to mold the blend.